Add support for static and random routing keys in kafka output (#4579)

plugins/outputs/kafka/README.md

@@ -50,6 +50,13 @@ This plugin writes to a [Kafka Broker](http://kafka.apache.org/07/quickstart.htm
   ##  ie, if this tag exists, its value will be used as the routing key
   routing_tag = "host"
 
+  ## Static routing key.  Used when no routing_tag is set or as a fallback
+  ## when the tag specified in routing tag is not found.  If set to "random",
+  ## a random value will be generated for each message.
+  ##   ex: routing_key = "random"
+  ##       routing_key = "telegraf"
+  # routing_key = ""
+
   ## CompressionCodec represents the various compression codecs recognized by
   ## Kafka in messages.
   ##  0 : No compression

plugins/outputs/kafka/kafka.go

@@ -10,6 +10,7 @@ import (
 	tlsint "github.com/influxdata/telegraf/internal/tls"
 	"github.com/influxdata/telegraf/plugins/outputs"
 	"github.com/influxdata/telegraf/plugins/serializers"
+	uuid "github.com/satori/go.uuid"
 
 	"github.com/Shopify/sarama"
 )
@@ -22,23 +23,15 @@ var ValidTopicSuffixMethods = []string{
 
 type (
 	Kafka struct {
-		// Kafka brokers to send metrics to
 		Brokers          []string
-		// Kafka topic
 		Topic            string
-		// Kafka client id
 		ClientID         string      `toml:"client_id"`
-		// Kafka topic suffix option
 		TopicSuffix      TopicSuffix `toml:"topic_suffix"`
-		// Routing Key Tag
 		RoutingTag       string      `toml:"routing_tag"`
-		// Compression Codec Tag
+		RoutingKey       string      `toml:"routing_key"`
 		CompressionCodec int
-		// RequiredAcks Tag
 		RequiredAcks     int
-		// MaxRetry Tag
 		MaxRetry         int
-		// Max Message Bytes
 		MaxMessageBytes  int `toml:"max_message_bytes"`
 
 		Version string `toml:"version"`
@@ -116,6 +109,13 @@ var sampleConfig = `
   ##  ie, if this tag exists, its value will be used as the routing key
   routing_tag = "host"
 
+  ## Static routing key.  Used when no routing_tag is set or as a fallback
+  ## when the tag specified in routing tag is not found.  If set to "random",
+  ## a random value will be generated for each message.
+  ##   ex: routing_key = "random"
+  ##       routing_key = "telegraf"
+  # routing_key = ""
+
   ## CompressionCodec represents the various compression codecs recognized by
   ## Kafka in messages.
   ##  0 : No compression
@@ -273,6 +273,22 @@ func (k *Kafka) Description() string {
 	return "Configuration for the Kafka server to send metrics to"
 }
 
+func (k *Kafka) routingKey(metric telegraf.Metric) string {
+	if k.RoutingTag != "" {
+		key, ok := metric.GetTag(k.RoutingTag)
+		if ok {
+			return key
+		}
+	}
+
+	if k.RoutingKey == "random" {
+		u := uuid.NewV4()
+		return u.String()
+	}
+
+	return k.RoutingKey
+}
+
 func (k *Kafka) Write(metrics []telegraf.Metric) error {
 	msgs := make([]*sarama.ProducerMessage, 0, len(metrics))
 	for _, metric := range metrics {
@@ -285,8 +301,9 @@ func (k *Kafka) Write(metrics []telegraf.Metric) error {
 			Topic: k.GetTopicName(metric),
 			Value: sarama.ByteEncoder(buf),
 		}
-		if h, ok := metric.GetTag(k.RoutingTag); ok {
+		key := k.routingKey(metric)
-			m.Key = sarama.StringEncoder(h)
+		if key != "" {
+			m.Key = sarama.StringEncoder(key)
 		}
 		msgs = append(msgs, m)
 	}

plugins/outputs/kafka/kafka_test.go

@@ -2,7 +2,10 @@ package kafka
 
 import (
 	"testing"
+	"time"
 
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/metric"
 	"github.com/influxdata/telegraf/plugins/serializers"
 	"github.com/influxdata/telegraf/testutil"
 	"github.com/stretchr/testify/require"
@@ -96,3 +99,59 @@ func TestValidateTopicSuffixMethod(t *testing.T) {
 		require.NoError(t, err, "Topic suffix method used should be valid.")
 	}
 }
+
+func TestRoutingKey(t *testing.T) {
+	tests := []struct {
+		name   string
+		kafka  *Kafka
+		metric telegraf.Metric
+		check  func(t *testing.T, routingKey string)
+	}{
+		{
+			name: "static routing key",
+			kafka: &Kafka{
+				RoutingKey: "static",
+			},
+			metric: func() telegraf.Metric {
+				m, _ := metric.New(
+					"cpu",
+					map[string]string{},
+					map[string]interface{}{
+						"value": 42.0,
+					},
+					time.Unix(0, 0),
+				)
+				return m
+			}(),
+			check: func(t *testing.T, routingKey string) {
+				require.Equal(t, "static", routingKey)
+			},
+		},
+		{
+			name: "random routing key",
+			kafka: &Kafka{
+				RoutingKey: "random",
+			},
+			metric: func() telegraf.Metric {
+				m, _ := metric.New(
+					"cpu",
+					map[string]string{},
+					map[string]interface{}{
+						"value": 42.0,
+					},
+					time.Unix(0, 0),
+				)
+				return m
+			}(),
+			check: func(t *testing.T, routingKey string) {
+				require.Equal(t, 36, len(routingKey))
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			key := tt.kafka.routingKey(tt.metric)
+			tt.check(t, key)
+		})
+	}
+}